System and method for controlling valve timing of continuous variable valve duration engine

ABSTRACT

A method for controlling intake and exhaust valves of an engine includes: controlling, by an intake continuous variable valve timing (CVVT) device, opening and closing timings of the intake valve; controlling, by an exhaust CVVT device, opening and closing timing of the exhaust valve; determining, by a controller, first to fifth control regions based on engine load and speeds, and a target opening duration of the intake valve and target opening or target closing timings of the intake valve; modifying, by an intake continuous variable valve duration (CVVD) device, current opening and closing timings of the intake valve based on the target opening duration; and advancing or retarding, by the intake CVVD device, the current opening timing of the intake valve while simultaneously retarding or advancing the current closing timing of the intake valve by a predetermined value based on the target opening duration of the intake valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 15/340,778, filed on Nov. 1, 2016, and claims priority to andthe benefit of Korean Patent Application Nos. 10-2015-0175141, filed onDec. 9, 2015, and 10-2017-0154705, filed on Nov. 20, 2017, the entiretyof each of which are incorporated herein by reference.

FIELD

The present disclosure relates to a system and a method for controllingvalve timing of a continuous variable valve duration engine.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

An internal combustion engine combusts mixed gas in which fuel and airare mixed at a predetermined ratio through a set ignition mode togenerate power by using explosion pressure.

Generally, a camshaft is driven by a timing belt connected with acrankshaft that converts linear motion of a piston by the explosionpressure into rotating motion to actuate an intake valve and an exhaustvalve, and while the intake valve is opened, air is suctioned into acombustion chamber, and while an exhaust valve is opened, gas which iscombusted in the combustion chamber is exhausted.

To improve the operations of the intake valve and the exhaust valve andthereby improve engine performance, a valve lift and a valveopening/closing time (timing) are controlled according to a rotationalspeed or load of an engine. Therefore, a continuous variable valveduration (CVVD) device controlling opening duration of an intake valveand an exhaust valve of the engine and a continuous variable valvetiming (CVVT) device controlling opening timing and closing timing ofthe intake valve and the exhaust valve of the engine have beendeveloped.

The CVVD device adjusts opening duration of the valve. In addition, theCVVT device advances or retards the opening and closing timing of thevalve in a state in which the duration of the valve is fixed. In otherwords, when the opening timing of the valve is determined, the closingtiming is automatically determined according to the duration of thevalve.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the disclosure andtherefore it may contain information that does not form the prior artthat is already known to a person of ordinary skill in the art.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

SUMMARY

The present disclosure provides a system and a method for controllingvalve timing of a continuous variable valve duration engine havingadvantages of simultaneously controlling duration and timing of thecontinuous variable valve by mounting a continuous variable valveduration device and a continuous variable valve timing device on anintake and mounting a continuous variable valve timing device on anexhaust.

In one form of the present disclosure, a method for controlling intakeand exhaust valves of an engine includes: controlling, by an intakecontinuous variable valve timing (CVVT) device, opening and closingtimings of the intake valve; controlling, by an exhaust CVVT device,opening and closing timing of the exhaust valve; determining, by acontroller, a target opening duration of the intake valve and at leastone of a target opening timing or a target closing timing of the intakevalve and the exhaust valve, based on an engine load and an enginespeed; modifying, by an intake continuous variable valve duration (CVVD)device, current opening and closing timings of the intake valve based onthe target opening duration of the intake valve; and advancing, by theintake CVVD device, the current opening timing of the intake valve whilesimultaneously retarding the current closing timing of the intake valveby a predetermined value, or retarding the current opening timing of theintake valve while simultaneously advancing the current closing timingof the intake valve by a predetermined value, based on the targetopening duration of the intake valve.

In particular, the intake CVVD device advances the current openingtiming of the intake valve while simultaneously retarding the currentclosing timing of the intake valve when the target opening duration ofthe intake valve is longer than a duration between the current openingtiming and current closing timing of the intake valve.

The intake CVVD device retards the current opening timing of the intakevalve while simultaneously advancing the current closing timing of theintake valve when the target opening duration of the intake valve isshorter than a duration between the current opening timing and currentclosing timing of the intake valve.

The method further includes the step of adjusting, by the intake CVVTdevice, the current opening and closing timings of the intake valve tothe target opening and closing timings of the intake valve,respectively.

During the step of determining the target opening duration of the intakevalve, the controller sets the target opening duration of the intakevalve to a first intake opening duration in a first control region wherethe engine load is between first and second predetermined loads, and thecontroller controls the intake CVVD device to adjust a current openingduration to the first intake opening duration and controls a valveoverlap between the intake valve and the exhaust valve in the firstcontrol region.

The current opening and closing timings of the intake valve are fixedand the closing timing of the exhaust valve is set as a maximum valuecapable of maintaining combustion stability in the first control region.

During the step of determining the target opening duration of the intakevalve, the controller sets the target opening duration of the intakevalve to a second intake opening duration in a second control regionwhere the engine load is greater than the second predetermined load andequal to or less than a third predetermined load, and the controllerreduces a valve overlap by advancing the current closing timing of theexhaust valve via the exhaust CVVT device in the second control region.

In one form, a retardation amount of the current closing timing of theexhaust valve is reduced based on an increase of the engine load in thesecond control region.

The method further includes the step of advancing the current closingtiming of the intake valve via the intake CVVT device according to anincrease of the engine load in a third control region where the engineload is greater than a third predetermined load and equal to or lessthan a fourth predetermined load.

The method further includes the step of controlling, by the controller,a throttle valve to be fully opened; and controlling the current closingtiming of the exhaust valve to be an angle after a top dead center (TDC)in a fourth control region where the engine load is greater than afourth predetermined load and equal to or less than a fifthpredetermined load and the engine speed is between first and secondpredetermined speeds.

In another form, the method may include: the step of determining a fifthcontrol region when the engine load is greater than a fourthpredetermined load and equal to or less than a fifth predetermined loadand the engine speed is greater than a second predetermined speed andequal to or less than a third predetermined speed; and the step ofcontrolling, by the controller, a throttle valve to be fully opened andthe current closing timing of the intake valve according to the enginespeed in the fifth control region.

The target opening duration of the intake valve is increased accordingto an increase of the engine speed by retarding the current opening andclosing timings of the intake valve in the fifth control region.

The exhaust CVVT device controls the current closing timing of theexhaust valve to be approximately at a top dead center so as to inhibita valve overlap in the fifth control region.

According to one form of the present disclosure, duration and timing ofthe continuous variable valve are simultaneously controlled, so theengine may be controlled under desirable conditions.

That is, since opening timing and closing timing of the intake valve andthe exhaust valve are appropriately controlled, the fuel efficiencyunder a partial load condition and power performance under a high loadcondition are improved. In addition, a fuel amount for starting may bereduced by increasing a valid compression ratio, and exhaust gas may bereduced by shortening time for heating a catalyst.

Further, a fixed cam may be used instead of a continuous variable valveduration device in the exhaust, thereby reducing the additional cost.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a schematic block diagram showing a system for controllingvalve timing of a continuous variable valve duration engine according toone form of the present disclosure;

FIG. 2 is a perspective view showing an intake provided with acontinuous variable valve duration device and a continuous variablevalve timing device and an exhaust provided with a continuous variablevalve timing device according to one form of the present disclosure;

FIG. 3 is a side view of a continuous variable valve duration deviceassembled with a continuous variable valve timing device in anotherform;

FIG. 4 is a partial view of an inner wheel and a cam unit of acontinuous variable valve duration device in one form;

FIGS. 5A-5C are views illustrating the operation of an intake continuousvariable valve duration device in FIG. 4;

FIGS. 6A and 6B are views illustrating a cam slot of an intakecontinuous variable valve duration device in exemplary forms;

FIGS. 7A-7C are valve profiles of an intake continuous variable valveduration device in one form;

FIGS. 8A-8D illustrate a change of an opening duration and opening andclosing timings of a valve;

FIGS. 9A and 9B are flowcharts showing a method for controlling valvetiming of a continuous variable valve duration engine according to oneform of the present disclosure;

FIG. 10 is a schematic diagram illustrating control regions in one form;

FIGS. 11A-11C are graphs showing duration, opening timing, and closingtiming of an intake valve depending on an engine load and an enginespeed in one form of the present disclosure; and

FIGS. 12A-12C are graphs showing duration, opening timing, and closingtiming of an exhaust valve depending on an engine load and an enginespeed in one form of the present disclosure.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

As those skilled in the art would realize, the described forms may bemodified in various different ways, all without departing from thespirit or scope of the present disclosure.

Throughout this specification and the claims which follow, unlessexplicitly described to the contrary, the word “comprise” and variationssuch as “comprises” or “comprising” will be understood to imply theinclusion of stated elements but not the exclusion of any otherelements.

It is understood that the term “vehicle” or “vehicular” or other similarterms as used herein is inclusive of motor vehicles in general includinghybrid vehicles, plug-in hybrid electric vehicles, and other alternativefuel vehicles (e.g., fuels derived from resources other than petroleum).As referred to herein, a hybrid electric vehicle is a vehicle that hastwo or more sources of power, for example a gasoline-powered andelectric-powered vehicle.

Additionally, it is understood that some of the methods may be executedby at least one controller. The term controller refers to a hardwaredevice that includes a memory and a processor configured to execute oneor more steps that should be interpreted as its algorithmic structure.The memory is configured to store algorithmic steps, and the processoris specifically configured to execute said algorithmic steps to performone or more processes which are described further below.

Furthermore, the control logic of the present disclosure may be embodiedas non-transitory computer readable media on a computer readable mediumcontaining executable program instructions executed by a processor, acontroller, or the like. Examples of computer readable media include,but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetictapes, floppy disks, flash drives, smart cards, and optical data storagedevices. The computer readable recording medium can also be distributedin network coupled computer systems so that the computer readable mediais stored and executed in a distributed fashion, e.g., by a telematicsserver or a controller area network (CAN).

FIG. 1 is a schematic block diagram showing a system for controllingvalve timing of a continuous variable valve duration engine according toan exemplary form of the present disclosure.

As shown in FIG. 1, a system for controlling valve timing of acontinuous variable valve duration engine according to an exemplary formof the present disclosure includes a data detector 100, a camshaftposition sensor 120, a controller 300, an intake continuous variablevalve duration device 400, an intake continuous variable valve timingdevice 450, an exhaust continuous variable valve timing device 550, anda throttle valve 600, although other sensors or systems may be employedto detect or determine the desired data.

The data detector 100 detects data related to a running state of thevehicle for controlling the CVVD device and the CVVT devices, andincludes a vehicle speed sensor 111, an engine speed sensor 112, an oiltemperature sensor 113, an air flow sensor 114, and an accelerator pedalposition sensor (APS) 115.

The vehicle speed sensor 111 detects a vehicle speed, and transmits asignal corresponding thereto to the controller 300. The vehicle speedsensor 111 may be mounted at a wheel of the vehicle.

The engine speed sensor 112 detects an engine speed from a change inphase of a crankshaft or camshaft, and transmits a signal correspondingthereto to the controller 300.

The oil temperature sensor (OTS) 113 detects temperature of oil flowingthrough an oil control valve (OCV), and transmits a signal correspondingthereto to the controller 300.

The oil temperature detected by the oil temperature sensor 113 may bedetermined by determining a coolant temperature using a coolanttemperature sensor mounted at a coolant passage of an intake manifold.Therefore, in one form, the oil temperature sensor 113 may include thecoolant temperature sensor, and the oil temperature should be understoodto be the coolant temperature.

The air flow sensor 114 detects an air amount flowing into the intakemanifold, and transmits a signal corresponding thereto to the controller300.

The accelerator pedal position sensor 115 detects a degree at which adriver pushes an accelerator pedal, and transmits a signal correspondingthereto to the controller 300. A position value of the accelerator pedalis 100% when the accelerator pedal is pressed fully, and the positionvalue of the accelerator pedal is 0% when the accelerator pedal is notpressed at all.

A throttle valve position sensor that is mounted on an intake passagemay be used instead of the accelerator pedal position sensor 115.Therefore, in one form, the accelerator pedal position sensor 115 mayinclude the throttle valve position sensor, and the position value ofthe accelerator pedal should be understood to be an opening value of thethrottle value.

The camshaft position sensor 120 detects a position of a camshaft angle,and transmits a signal corresponding thereto to the controller 300.

FIG. 2 is a perspective view showing an intake provided with acontinuous variable valve duration device and a continuous variablevalve timing device and an exhaust provided with a continuous variablevalve timing device according to one form of the present disclosure.

As shown in FIG. 2, the continuous variable valve duration device andthe continuous variable valve timing device are mounted on the intake,and the continuous variable valve timing device is mounted on theexhaust through a fixed cam. Therefore, exhaust valve duration (EVD) isfixed. If the EVD becomes long, fuel efficiency and high speedperformance of the vehicle may be improved, but low speed performancemay be deteriorated. Thus, the EVD may be fixed at an angle ofapproximately 220 to 240 degrees.

The intake continuous variable valve duration (CVVD) device 400 controlsopening duration of an intake valve of the engine according to a signalfrom the controller 300.

FIG. 3 is a side view of the intake CVVD device in another form asassembled with the intake CVVT for intake valves 200 operating withcylinders 201, 202, 203, 204. In one form, two cams 71 and 72 may beformed on first and second cam portions 70 a and 70 b, and a cam capengaging portion 76 may be formed between the cams 71 and 72 andsupported by a cam cap 40. The valve 200 is opened and closed by beingin contact with the cams 71 and 72.

As illustrated in FIG. 3, the intake CVVD device includes: a cam unit 70in which a cam 71 is formed and into which a cam shaft 30 is inserted;an inner wheel 80 to transfer the rotation of the cam shaft 30 to thecam unit 70 (See, in FIG. 4); a wheel housing 90 in which the innerwheel 80 rotates and movable in a direction perpendicular to thecamshaft 30; a guide shaft 132 having a guide thread and provided in adirection perpendicular to the camshaft 30, the guide shaft mounted by aguide bracket 134; a worm wheel 50 having an inner thread engaged withthe guide thread and disposed inside the wheel housing 90; and a controlshaft 102 formed with a control worm 104 meshing with the worm wheel 50.The control worm 104 is engaged with an outer thread formed on the outerside of the worm wheel 50. The intake CVVD device further includes asliding shaft 135 fixed to the guide bracket 134 and guiding themovement of the wheel housing 90.

FIG. 4 is a partial view of the inner wheel 80 and the cam unit 70 ofthe intake CVVD device of the FIG. 3. Referring to FIG. 4, First andsecond sliding holes 86 and 88 are formed in the inner wheel 80, and acam slot 74 is formed in the cam unit 70.

The intake CVVD device further includes: a roller wheel 60 inserted intothe first sliding hole 86 allowing the roller wheel 60 to rotate; and aroller cam 82 inserted into the cam slot 74 and the second sliding hole88. The roller cam 82 may slide in the cam slot 74 and rotate in thesecond sliding hole 88.

The roller cam 82 includes: a roller cam body 82 a slidably insertedinto the cam slot 74 and a roller cam head 82 b rotatably inserted intothe second sliding hole 88.

The roller wheel 60 includes: a wheel body 62 slidably inserted into thecamshaft 30 and a wheel head 64 rotatably inserted into the firstsliding hole 86. A cam shaft hole 34 is formed in the camshaft 30 and awheel body 62 of the roller wheel 60 is movably inserted into thecamshaft hole 34.

FIGS. 5A-5C illustrate the operation of the intake CVVD device. FIG. 5Aillustrates a neutral state in which the rotational center of thecamshaft 30 and the cam unit 70 coincide with each other. In this case,the cams 71 and 72 rotate at the same speed as the camshaft 30. When thecontroller 300 applies a control signal based on engine load and/orengine speed, a control motor 106 rotates the control shaft 102. Then,the control worm 104 rotates the worm wheel 50 which in turn rotates andmoves along the guide thread formed on the guide shaft 132.

As a result, the worm wheel 50 causes a change to a position of thewheel housing 90 relative to the cam shaft 30. As illustrated in FIGS.5B and 5C, when the position of the wheel housing 90 moves in onedirection with respect to the center of rotation of the camshaft 30, therotational speed of the cams 71, 72 with respect to the camshaft 30 arechanged in accordance with their phases. FIG. 7A and FIG. 8B aredrawings showing a valve profile illustrating valve opening durationchange by the operation of the intake CVVD device. The solid linerepresents a general valve profile (e.g., a current opening duration),and the dotted line shows the valve profile as a short opening duration(e.g., a target opening duration in FIG. 8B) is applied. FIG. 8Aillustrates a changed valve profile when the long opening duration isapplied by the CVVD device. The controller 300 determines a targetopening duration based on an engine load and an engine speed andcontrols the intake CVVD device to modify current opening and closingtimings of the intake valve based on the target opening duration.

More specifically, as illustrated in FIG. 8B, the intake CVVD device mayretard the current opening timing of the intake valve whilesimultaneously advancing the current closing timing of the intake valveto shorten the opening duration according to a predetermined valueprovided by the controller 300. When the controller applies a longeropening duration (i.e., a target opening duration) than the currentopening duration, as illustrated in FIG. 8A, the CVVD device may advancethe current opening timing of the intake valve while simultaneouslyretarding the current closing timing of the intake vale so that themodified opening duration becomes longer than the current openingduration. FIGS. 8C and 8D illustrate the relationship between theoperation of the CVVD device and the CVVT device. As discussed above,the CVVD device may change the opening duration of a valve (e.g., intakeor exhaust valve) whereas the CVVT device may shift a valve profileaccording to a target opening and/or a target closing timings withoutchange to the period of the valve opening duration. It should be notedthat the changing opening duration by the CVVD device may occur afterchanging valve opening and/or closing timings of intake or exhaustvalves by the CVVT device. In another form, the operation of the CVVTdevice to change the opening and closing timings may occur after theoperation of the CVVD device. In still another form, the operation ofthe CVVD and CVVT devices may perform simultaneously to change theopening duration and the timing of opening and closing of intake orexhaust valves.

FIGS. 6A and 6B illustrate a view of the cam slot 74 a, 74 b of theintake CVVD device, and FIGS. 7A-7C illustrate valve profiles of theCVVD device in exemplary forms of the present disclosure.

Referring to FIGS. 6A-6B, the cam slot 74 a may be formed in an advancedposition relative to the cam 71, 72, or in another form the cam slot 74b may be formed in a retarded position relative to the cam 71, 72. Inanother form, the cam slot 74 a, 74 b may be formed to have the samephase as the lobe of the cam 71, 72. These variations are enable torealize various valve profiles. Based on the position of the cam slot 74a, 74 b, and a contact position between the cam and the intake valve,the opening and closing timings of the intake valve may vary. FIG. 7Bshows that the intake CVVD device may advance (for a short openingduration) or retard the current closing timing (for a long openingduration) of the intake valve by a predetermined value based on thetarget opening duration of the intake valve while maintaining thecurrent opening timing of the intake valve. In another form, asillustrated in FIG. 7C, the intake CVVD device may advance (for a longopening duration) or retard (for a short opening duration) the currentopening timing of the intake valve by a predetermined value based on thetarget opening duration of the intake valve while maintaining thecurrent closing timing of the intake valve.

The intake continuous variable valve timing (CVVT) device 450 controlsthe opening timing and closing timing of the intake valve of the engineaccording to a signal from the controller 300, and the exhaustcontinuous variable valve timing (CVVT) device 550 controls the openingtiming and closing timing of an exhaust valve of the engine according toa signal from the controller 300.

The throttle valve 600 adjusts the amount of air flowing into the intakemanifold.

The controller 300 classifies a plurality of control regions dependingon an engine speed and an engine load based on signals of the datadetector 100 and the camshaft position sensor 120, and controlsoperations of the intake CVVD device 400, the intake CVVT device 450,the exhaust CVVT device 550, and the throttle valve 600. Herein, theplurality of control regions may be classified into five regions.

The controller 300 applies a maximum duration (i.e., a target openingduration) to the intake valve and controls valve overlap between theexhaust valve and the intake valve in a first control region, appliesthe maximum duration to the intake valve and controls the valve overlapto be reduced by using exhaust valve closing (EVC) timing in a secondcontrol region, advances intake valve closing (IVC) timing according toan increase of the engine load in a third control region, controls thethrottle valve to be fully opened and controls the EVC timing to anangle after top dead center (TDC) in a fourth control region, andcontrols the throttle valve to be fully opened and controls the IVCtiming according to the engine speed in a fifth control region.

For these purposes, the controller 300 may be implemented with at leastone processor executed by a predetermined program, and the predeterminedprogram may programmed in order to perform each step of a method forcontrolling valve timing of a continuous variable valve duration engine.

Various forms described herein may be implemented within a recordingmedium that may be read by a computer or a similar device by usingsoftware, hardware, or a combination thereof.

For example, the hardware of the forms described herein may beimplemented by using at least one of application specific integratedcircuits (ASICs), digital signal processors (DSPs), digital signalprocessing devices (DSPDs), programmable logic devices (PLDs), fieldprogrammable gate arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, and electrical units designed toperform any other functions.

The software such as procedures and functions of the forms described inthe present disclosure may be implemented by separate software modules.Each of the software modules may perform one or more functions andoperations described in the present disclosure. A software code may beimplemented by a software application written in an appropriate programlanguage.

Hereinafter, a method for controlling valve timing of a continuousvariable valve duration engine according to one form of the presentdisclosure will be described in detail with reference to FIG. 9A to FIG.12C.

FIGS. 9A and 9B are flowcharts showing a method for controlling valvetiming of a continuous variable valve duration engine. FIG. 10 is aschematic block diagram of showing control regions based on engine load(e.g., engine torque) and engine speed. In addition, FIGS. 11A-11C aregraphs showing duration, opening timing, and closing timing of an intakevalve depending on an engine load and an engine speed, and FIGS. 12A-12Care graphs showing duration, opening timing, and closing timing of anexhaust valve depending on an engine load and an engine speed.

As shown in FIGS. 9A and 9B, a method for controlling valve timing of acontinuous variable valve duration engine begins with classifying aplurality of control regions depending on an engine load and an enginespeed at step S100. The control region may be divided into five controlregions (e.g., first, second, third, fourth, and fifth control regions).The first to fifth control regions are indicated in FIG. 10, and FIG.11A to FIG. 12C in more detail. FIG. 10 schematically describes thecontrol regions based on the engine load (e.g., engine torque) andengine speed (e.g., revolutions per minutes “rpm”). However, the controlregions may vary based on engine type or engine size. Mixed control maybe performed at the boundary of each region to minimize the controlimpact of the engine. Accordingly, the range of each region shown in thepresent application is exemplary, and the classification of each regionmay be varied.

The controller 300 may determine a control region as the first controlregion (namely, {circle around (1)} an idling region and low-loadcondition) when the engine load is between a first predetermined load(e.g., a minimum engine torque) and a second predetermined load, asecond control region (namely, {circle around (2)} an mid-loadcondition) when the engine load is greater than the second predeterminedload and equal to or less than a third predetermined load, and a thirdcontrol region (namely, {circle around (3)} a high-load condition) wherethe engine load is greater than the third predetermined load and lessthan a fourth predetermined load.

In addition, the controller 300 may determine a control region as thefourth control region (namely, {circle around (4)} a low-speed wide openthrottle “WOT” condition) when the engine load is greater than thefourth predetermined load (i.e., a maximum torque at the idle rpm) andequal to or less than the fifth predetermined load (i.e., a maximumtorque) and the engine speed is between a first predetermined speed(i.e., the idle rpm) and a second predetermined speed, and determine thefifth control region (namely, {circle around (5)} a mid-high speed WOTcondition) when the engine load is greater than the fourth predeterminedload and equal to or less than the fifth predetermined load and theengine speed is greater than the second predetermined speed and equal toor less than a third predetermined speed (i.e., an engine maximum rpm).

Referring to FIG. 10, the first predetermined load (e.g., a minimumengine torque) is measured when a input from the APS is zero “0,” andthe second to fifth predetermined loads, and the second and thirdpredetermined engine speeds may be calculated by the followingequations:Second predetermined load=min_L+((⅖)×(max_L@idle_rpm-min_L);Third predetermined load=min_L+(⅘)×(max_L@idle_rpm−min_L);Fourth predetermine load=max_L@idle_rpm;Fifth predetermined load=max_L;Second predetermined engine speed=min_S+( 3/10)×(max_S−min_S); andThird predetermined engine speed=max_S,

where, min_L is the minimum engine torque; max_L@idle_rpm is a maximumengine torque at a minimum engine rpm (i.e., Idle rpm); max_L is amaximum engine torque; min_S is a minimum engine rpm (e.g., Idle rpm);and max_S is a maximum engine rpm.

Meanwhile, as shown in FIG. 11A to FIG. 12C, a crank angle is indicatedin intake valve duration (IVD) map and an exhaust valve duration (EVD)map. For example, regarding the IVD map, a curved line indicated by‘200’ in the fifth control region means that the crank angel isapproximately 200 degrees, and a curved line indicated by ‘220’ meansthat the crank angle is approximately 220 degrees. Although notillustrated in FIG. 11A-11C, a curved line having a crank angle betweenapproximately 200 and 220 degrees may exist between the curved lines.

In addition, a number designated in an intake valve opening (IVO) timingmap represents before top dead center (TDC), a number designated anintake valve closing (IVC) timing map represents after bottom deadcenter (BDC), a number designated in an exhaust valve opening (EVO)timing map represents before BDC, and a number designated in an exhaustvalve closing (EVC) timing map represents after TDC.

Regions and curved lines shown in FIG. 11A to FIG. 12C are just examplesfor describing one form of the present disclosure, and the presentdisclosure is not limited thereto.

When the control regions are classified depending on the engine load andthe engine speed at step S100, the controller 300 determines whether acurrent engine state belongs to the first control region at step S110.

When the engine load is between a first predetermined load (i.e.,minimum load, or idle load) and the second predetermined load at stepS110, the controller 300 determines that the current engine statebelongs to the first control region. In this case, the controller 300applies the maximum duration or a first intake opening duration to theintake valve and controls the valve overlap between the exhaust valveand the intake valve at step S120. The valve overlap represents a statein which the intake valve is opened and the exhaust valve is not yetclosed.

In other words, when the engine is operated at a low load condition, thecontroller 300 may fix the IVO timing and the IVC timing to apply themaximum duration to the intake valve. In other words, the controller 300controls the intake CVVD device to adjust a current opening duration tothe first intake opening duration by advancing the IVO timing andretarding the IVC timing. As shown in FIGS. 11B and 11C, the IVO timingmay be fixed at an angle of approximately 0 to 10 degrees before TDC,and the IVC timing may be fixed at an angle of approximately 100 to 110degrees after BDC.

In addition, the controller 300 may set the EVC timing as a maximumvalue capable of maintaining combustion stability by moving the EVCtiming in an after TDC direction. As the valve overlap is increased,fuel efficiency may be improved, but combustion stability may bedeteriorated. Accordingly, properly setting of the valve overlap isdesired. By setting the EVC timing as the maximum value capable ofmaintaining combustion stability, a valve overlap may be realized, andthus fuel efficiency may be improved.

When the current engine state does not belong to the first controlregion at step S110, the controller 300 determines whether the currentengine state belongs to the second control region at step S130. However,each of the control regions may be determined immediately by thecontroller 300 based on the engine load and/or engine speed.

When the engine load is greater than the second predetermined load andequal to or less than the third predetermined load at step S130, thecontroller 300 determines that the current engine state belongs to thesecond control region. In this case, the controller 300 applies themaximum duration to the intake valve and controls the valve overlap tobe reduced by using the EVC timing at step S140.

When the EVC timing is retarded in the after TDC direction, as the valveoverlap is increased, intake pumping may be decreased, however, sincethe exhaust valve duration (EVD) is fixed, exhaust pumping may beincreased as the EVO timing approaches BDC. In addition, the exhaustpumping may be increased as the engine load is increased in the secondcontrol region. Accordingly, the controller 300 may reduce the valveoverlap by reducing retardation amount of the EVC timing according to anincrease of the engine load.

In addition, the controller 300 may apply the maximum duration to theintake valve to prevent or inhibit knocking according to the increase ofthe engine load, and maintain a late intake valve close (LIVC) positionat the angle of approximately 100 to 110 degrees after BDC.

When the current engine state does not belong to the second controlregion at step S130, the controller 300 determines whether the currentengine state belongs to the third control region at step S150.

When the engine load is greater than a third predetermined load andequal to or less than a fourth predetermined load (i.e., a maximumtorque at engine idle rpm), the controller 300 determines that thecurrent engine state belongs to the third control region. In this case,the controller 300 advances the IVC timing according to the increase ofthe engine load at step S160.

In this case, the controller 300 may fix the exhaust CVVT device at alocking position by fixing the EVC timing.

When the current engine state does not belong to the third controlregion at step S150, the controller 300 determines whether the currentengine state belongs to the fourth control region at step S170. Inanother form, the controller 300 may determine the condition for thefourth control region without performing the step of determining thefirst, second and third control regions.

The controller 300 determines that the current engine state belongs tothe fourth control region when the engine load is greater than thefourth predetermined load and equal to or less than a fifthpredetermined load (i.e., engine maximum torque) and the engine speed isbetween a first predetermined speed (i.e., idle rpm) and a secondpredetermined speed. In this case, the controller 300 controls thethrottle valve to be fully opened and controls the EVC timing to anangle after TDC at step S180.

Since the engine speed is less than the predetermined speed (e.g.,approximately 1500 rpm) in the fourth control region, the EVO timingshould be close to BDC so as to reduce exhaust interference. Since theEVD is fixed in one form of the present disclosure, the controller 300may control the EVC timing to an angle after TDC.

When the current engine state does not belong to the fourth controlregion at step S170, the controller 300 determines whether the currentengine state belongs to the fifth control region at step S190.

When the engine load is greater than the fourth predetermined load andequal to or less than the fifth predetermined load and the engine speedis greater than the second predetermined speed and equal to or less thana third predetermined speed (i.e., a maximum rpm) at step S190, thecontroller 300 determines that the current engine state belongs to thefifth control region. In this case, the controller 300 controls thethrottle valve to be fully opened and controls the IVC timing accordingto the engine speed at step S200.

The controller 300 may increase the IVD according to the increase of theengine speed by retarding the IVO timing and the IVC timing. Since theIVC timing may be a significant factor in the fifth control region wherethe engine speed is equal to or greater than the predetermined speed(e.g., approximately 1500 rpm), the IVC timing is firstly controlled toa desired value according to the engine speed. The IVC timing may begradually retarded from an angle of approximately 20 degrees to an angleof approximately 60 degrees after BDC according to the increase of theengine speed.

In this case, the controller 300 may generate a valve underlap byretarding the IVO timing in a medium speed (e.g., approximately1500-3000 rpm). Accordingly, the IVD may be decreased and then increasedwhen the engine speed increases.

In addition, the controller 300 may control the EVC timing to be closeto the TDC to prevent from generating the valve overlap.

Since a scavenging phenomenon that has occurred in the fourth controlregion disappears or is reduced as the exhaust pressure is increased,the valve overlap needs not to be generated. Accordingly, the controller300 controls the EVC timing to be close to TDC.

Since the EVD is fixed in one form of the present disclosure, thecontroller 300 may control the EVO timing to an angle of approximately40 to 50 degrees before BDC that is advantageous to exhaust pumping.

As described above, according to one form of the present disclosure,duration and timing of the continuous variable valve are simultaneouslycontrolled, so the engine may be controlled under desired conditions.

That is, since opening timing and closing timing of the intake valve andthe exhaust valve are appropriately controlled, the fuel efficiencyunder a partial load condition and power performance under a high loadcondition are improved. In addition, a fuel amount for starting may bereduced by increasing a valid compression ratio, and exhaust gas may bereduced by shortening time for heating a catalyst.

Since a fixed cam is used instead of a continuous variable valveduration device at the exhaust, production cost may be reduced withmaintaining power performance.

While this disclosure has been described in connection with what ispresently considered to be practical forms, it is to be understood thatthe disclosure is not limited to the disclosed forms, but, on thecontrary, is intended to cover various modifications and equivalentarrangements included within the spirit and scope of the presentdisclosure.

The description of the disclosure is merely exemplary in nature and,thus, variations that do not depart from the substance of the disclosureare intended to be within the scope of the disclosure. Such variationsare not to be regarded as a departure from the spirit and scope of thedisclosure.

What is claimed is:
 1. A method for controlling an intake valve and anexhaust valve of an engine, the method comprising: controlling, by anintake continuous variable valve timing (CVVT) device, opening andclosing timings of the intake valve; controlling, by an exhaust CVVTdevice, opening and closing timings of the exhaust valve; determining,by a controller, a target opening duration of the intake valve;determining, by the controller, at least one of a target opening timingof the intake valve, a target closing timing of the intake valve, atarget opening timing of the exhaust valve, or a target closing timingof the exhaust valve, based on an engine load and an engine speed; andadvancing, by an intake continuous variable valve duration (CVVD)device, a current opening timing of the intake valve by a firstpredetermined value while simultaneously retarding a current closingtiming of the intake valve by a second predetermined value and whilemaintaining a maximum amount of a valve lift of the intake valve at asame level, based on the target opening duration of the intake valve, orretarding the current opening timing of the intake valve by a thirdpredetermined value while simultaneously advancing the current closingtiming of the intake valve by a fourth predetermined value and whilemaintaining the maximum amount of the valve lift of the intake valve atthe same level, based on the target opening duration of the intakevalve, wherein, during the step of determining the target openingduration of the intake valve, the controller sets the target openingduration of the intake valve to a first intake opening duration in afirst control region where the engine load is between first and secondpredetermined loads, the controller sets the target opening duration ofthe intake valve to a second intake opening duration in a second controlregion where the engine load is greater than the second predeterminedload and equal to or less than a third predetermined load, and thecontroller controls the intake CVVD device to adjust a current openingduration to the first intake opening duration or the second intakeopening duration and controls a valve overlap between the intake valveand the exhaust valve in the first and second control regions, whereinthe first and second intake opening durations in the first and secondcontrol regions correspond to a maximum duration of the intake valve andare respectively obtained by setting the current opening timing of theintake valve in the first and second control regions to be earlier thanopening timings of the intake valve in other control regions and settingthe current closing timing of the intake valve to be later than closingtimings of the intake valve in the other control regions, and theclosing timing of the exhaust valve is set as a maximum value capable ofmaintaining combustion stability in the first control region, andwherein, the controller reduces the valve overlap by advancing thecurrent closing timing of the exhaust valve via the exhaust CVVT devicein the second control region where the engine load is greater than thesecond predetermined load compared to the first control region where theengine load is greater than the first predetermined load.
 2. The methodof claim 1, wherein the intake CVVD device advances the current openingtiming of the intake valve while simultaneously retarding the currentclosing timing of the intake valve when the target opening duration ofthe intake valve is longer than a duration between the current openingtiming and the current closing timing of the intake valve.
 3. The methodof claim 1, wherein the intake CVVD device retards the current openingtiming of the intake valve while simultaneously advancing the currentclosing timing of the intake valve when the target opening duration ofthe intake valve is shorter than a duration between the current openingtiming and the current closing timing of the intake valve.
 4. The methodof claim 1, further comprising the step of adjusting, by the intake CVVTdevice, the current opening and closing timings of the intake valve tothe target opening and closing timings of the intake valve,respectively.
 5. The method of claim 1, wherein a retardation amount ofthe current closing timing of the exhaust valve is reduced based on anincrease of the engine load in the second control region.
 6. The methodof claim 1, further comprising the step of advancing the current closingtiming of the intake valve via the intake CVVT device according to anincrease of the engine load in a third control region where the engineload is greater than the third predetermined load and equal to or lessthan a fourth predetermined load.
 7. The method of claim 1, furthercomprising the step of controlling, by the controller, a throttle valveto be fully opened; and controlling the current closing timing of theexhaust valve to be an angle after a top dead center (TDC) in a fourthcontrol region where the engine load is greater than a fourthpredetermined load and equal to or less than a fifth predetermined loadand the engine speed is between first and second predetermined speeds.8. The method of claim 1, further comprising the step of determining afifth control region when the engine load is greater than a fourthpredetermined load and equal to or less than a fifth predetermined loadand the engine speed is greater than a second predetermined speed andequal to or less than a third predetermined speed; and controlling, bythe controller, a throttle valve to be fully opened and the currentclosing timing of the intake valve according to the engine speed in thefifth control region.
 9. The method of claim 8, wherein the targetopening duration of the intake valve is increased according to anincrease of the engine speed by advancing the current opening timing ofthe intake valve and retarding the closing timing of the intake valve inthe fifth control region.
 10. The method of claim 8, wherein the exhaustCVVT device controls the current closing timing of the exhaust valve tobe approximately at a top dead center so as to inhibit the valve overlapin the fifth control region.